Attendance at scientific congresses is usually greatly appreciated by researchers, as it allows them to keep up to date in their area of knowledge or speciality and gives them an ideal framework for establishing the necessary contacts to promote and set up collaborations .
The percentage of subsequent publications from the abstracts presented to the 1999 CPDD meeting (36.9%) is similar to that found in a systematic review, showing that only one-third of the abstracts presented in biomedical meetings were published in medical journals . This percentage is a bit lower than the percentage found in Scherer's study across many different biomedical fields (44.5%) . In a recent study by Vecchi et al.  based on abstract presented to CPDD meetings between 1993 to 2002, and looking specifically at randomized controlled trials and controlled clinical trials, 62% of these abstracts were published in medical journals.
Oral communications presented at the CPDD meeting were more likely to be subsequently published in peer-reviewed journals than the posters, as has been observed in Radiology . This difference could be due to the fact that abstracts describing study results that are closer to completion, or completed, tend to be selected by the program committee for an oral presentation while more preliminary researches are selected for a poster.
The average time elapsed between abstract presentation at the 1999 CPDD Meeting and publication was 672.97 days, with a median of 598 days (19.9 months) similar to that observed in the area of Clinical Pharmacology and Pharmacoepidemiology (18 and 20 months, respectively) [12, 13]. Almost one third of the communications (72.55%) were published within the 24 months following the celebration of the congress, a higher percentage than that found in the work of Autorino et al and Dhaliwal et al  (with 58.8% and 15.6% respectively).
The time elapsed until publication of the study has no connection with the type of abstract presentation, as reported in the area of Paediatrics . However, it is related to the type of population studied, studies not carried out with humans being published earlier. It is our belief that this may be due to the fact that studies carried out with humans more often refer to preliminary results and/or partial samples when being presented at congresses, and also to the fact that the data collection process for human studies takes longer, especially for treatment-related studies.
The average number of authors per published article is greater (0.35) than the average per abstract presented at the CPDD congress. This could be due to the fact that the teams need a greater number of professionals to write a scientific article or that new professionals join the research teams.
The results obtained show a greater tendency towards collective authorships and, in some cases, for authors of different nationalities or from different centres. This fact can be fairly positive in the following aspects: reflecting collaboration between authors, the strengthening of work groups and the increased scientific communication, all fundamental elements for scientific development .
The wide range of journals publishing abstracts presented in congresses has already been observed in other areas, such as pharmacoepidemiology . This could probably be explained because research into substance abuse is multidisciplinary and is related to such disciplines as Neurology, Neurosciences, Psychopharmacology, Pharmacology, Psychiatry, Internal Medicine and Public Health.
Psychopharmacology was the journal that published the greatest number of articles, followed by Drug and Alcohol Dependence, the "parent" journal from the CPDD society. We are not able to provide an explanation of why these journals were selected by authors, but some aspects, such as their multidisciplinary approach, international audience and high impact factor, among other aspects, could be several of the reasons. Similar results were found in Vecchi et al.  study, in which CPDD meetings abstracts based on clinical trials were published mainly in Drug and Alcohol Dependence, Journal of Consulting and Clinical Psychology, and Psychopharmacology.
The impact factor is an important issue for this study due to the close relationship between the impact and the repercussions of the work, and even its quality. The journals with the greatest impact factor are also considered to be those of the greatest quality. The greater the number of communications subsequently published as articles in journals with high impact factors, the greater the quality of the scientific content of the congress will be.
The mean impact factor of the journals that published the articles between 1999-2005 was 2.82, a value greater than that of journals included in the subject category of Substance Abuse in the Journal Citation Report over the period under study (1.24), and greater than that found in publications following Paediatrics congresses . Nevertheless, it is similar to the mean of Gastroenterology (2.9)  and lower than that of Pharmacology (3.0)  and Vascular (3.5) . The fact that the mean value of the impact factor of the journals publishing the CPDD Meeting presentations is greater than that of the journals covering the area of Substance Abuse themselves is because some presentations were published in Psychiatry (Archives of General Psychiatry, 11.53) and Internal Medicine (Annals of Internal Medicine, 11.61) journals with high values.
As for the country of publication of the journals, it has been found that they are predominantly Anglo-American, which may be because most professionals attending the CPDD Meeting belong to that geographical area and because the Medline database includes mainly English language journals.
This study has some limitations that should be taken into account when interpreting the results. It examines only the 1999 CPDD meeting, so any trends could not be identified and it is unknown whether this represents a typical year or whether it is unusual. A further limitation is that the search was only carried out in Medline. This could mean that relevant studies may not be retrieved because that database does not include all the articles published in journals included in the Substance Abuse category of the Journal Citation Report® (for instance, from the Journal of Drug Issues only 17 articles are included), or these articles are published in non-English language journals not covered by Medline. However, Medline is one of the most important electronic databases in Health Sciences, so just like other authors, we believe that few publications have been missed , but the possibility of underestimation of publication rate because the limiting of the search to a single database could not be discharged. Like in previous studies [16, 19] we used the same criteria to perform only a Medline search when assessing the subsequent publication of the papers presented in Meetings. Another possible limitation is that changes may have occurred in the title of the articles or in the research teams that have resulted in the subsequent publication of a work being unrecognizable.
The subsequent publication of the abstracts presented in the CPDD meetings should be actively encouraged, because publication in journals is the culmination of scientific effort . It is the most important way in which scientific information is disseminated, both quantitatively and qualitatively [21, 22]. It is also the way junior and senior researchers have to attain recognition  so as to gain promotion in their professional careers and allows the economic funding dedicated to research to be used most profitably.
Actually, we can think of at least a couple reasons. One is that many of these studies have been sponsored by funding agencies or internal funds from Universities. Maximizing the dissemination of the results would help to maximize the value of the money spent. Thus, from the funder's perspective, not providing a maximum level of dissemination through publication detracts from their investment. Another reason has to do with promoting junior authors who often use presentations as a stepping stone in their career. Not publishing a publishable manuscript is to their detriment (and the detriment of their graduating University).
Overall, the publication patterns of the abstracts presented at the 1999 CPDD meeting do not differ from those observed in the Congresses of other areas of health sciences, as one in three communications presented at the 1999 CPDD meeting were published in peer-reviewed journals indexed in Medline.